Pouring of melts

ABSTRACT

In pouring superheated metal melts from a pouring vessel into an ingot mould or a chill mould, the molten metal is passed through a teeming tube of relatively small cross-sectional area into the mould, and during this passage the whole of the superheat and part of the heat of fusion is withdrawn from the melt, and measurements of the temperature of the melt are made at certain points in the teeming tube and employed for controlling the flow of the molten metal.

United States Patent [72] Inventor Kristof Tromel Buederich nearDuesseldorf, Germany [21] Appl. No. 815,954 [22] Filed Apr. 14, 1969[45] Patented Mar. 16, 1971 {73] Assignee Schloemann AktiengesellschaftDuesseldorf, Germany [32] Priority Mar. 9, 1965 [33] Germany [31] Sch36656 Continuation-impart of application Ser. No. 532,638, Mar. 8, 1966,now abandoned.

[54] POURING OF MELTS 10 Claims, 6 Drawing Figs.

[52] U.S. Cl 222/1, 222/54, 222/146, 222/566, 164/122 [51] Int. Cl B67d5/62 [50] Field ofSearch 222/1, 54, 146 (H), 146 (C), 566; 164/122, 337;266/38 [56] References Cited UNITED STATES PATENTS 770,130 9/1904 Trote164/270 958,613 5/1910 Forgo 65/25 Harrison Alexanderson Jones SeigfriedSteigerwald Eliot Brick et a1.

Miller et al. Woodburn, Jr... Calderon Primary Examiner-Robert B. ReevesAssistant Examiner-H. S. Lane Att0rney Holman, Glascock, Downing &Seebold PATENTED MAR] 6197! SHEET 1 BF 3 3 mm n Em? a Tx m N o J T 0 m.-K p. v B

PATENTEDHARIBIBH 3570.713

, SHEET 3 or 3 Fig. 6"

INVENTOR. KRISTOF TROMEL BYMMW M,

POURING OF MELTS This application is a continuation-in-part of myapplication Ser. No. 532,638 filed Mar. 8, 1966, now abandoned.

According to the present invention, the pouring or casting output in thepouring of a metal melt into an ingot mould or into a chill mould isincreased by withdrawing from the metal melt, on its way to the ingotmould or chill mould, its superheat, and also part of its heat offusion. The molten metal is passed through a teeming tube, which is ofsmall cross-sectional area in comparison with the ingot mould or chillmould, the pouring tube being cooled, and being traversed by the moltenmetal in turbulent flow, with a coefficient above its critical Reynoldsnumber. Under these circumstances temperatures which correspond to thetemperatures of the melt are measured at least at two positions locatedone behind the other in the direction of flow of the melt, and arecompared with one another.

The present patent application is a continuation-in-part of the US. Pat.Application Ser. No. 532,638, dated Mar. 8, 1966, now abandonedaccording to which it had already been proposed to withdraw thesuperheat from the metal melt, on its way to the ingot mould or chillmould by cooling, and to measure the temperature of the pouring jet atthe end of the cooling operation, and to control the speed of pouringand/or the cooling power by corresponding measurement of temperature.Amongst other things it had also already been proposed to employ athermocouple in the pouring tube in the neighborhood of the surface ofthe bath in the mould.

The present invention relates to further measures for increasing thecooling power, which consist in the feature that the molten metal ispassed through a teeming tube the crosssectional area of which is smallcompared with that of the ingot mould or chill mould, wherein the wholeof its superheat, and also a part of its heat of fusion, are withdrawnfrom it in the teeming tube by cooling, while it is flowing through theteeming tube in turbulent flow with a coefficient above the criticalReynolds number and temperatures corresponding to its temperature aremeasure at least at two places following one another in the direction offlow of the melt, and are compared with one another. In this way it ispossible to adjust the thermal content of the molten metal with greatprecision at its entry into the ingot mould or chill mould. Since themelt in the teeming tube is in a condition of turbulent flow, a smallpart of its heat of fusion can in fact be withdrawn at this position, sothat it may already contain to a certain extent presolidified metalparticles, without this leading to the teeming tube freezing up. In thiscase it is possible to withdraw about to percent of the heat of fusionfrom the melt. The turbulent condition of flow not only has the resultthat upon a withdrawal of part of the heat of fusion, freezing is stillnot possible, but in addition it also renders possible a betterutilization of the cooling power of the teeming tube. By comparing thevalues of the measured temperatures, as is still to be explained indetail, to fix exactly what part of the heat of fusion should bewithdrawn at each moment of the teeming operation.

The invention will now be further explained by way of illustration butnot of restriction, with reference to the accompanying diagrammaticdrawings, in which:

FIG. 1 shows a thermal-content diagram of a metal melt;

FIG. 2 shows a teeming tube with a cooling jacket;

FIG. 3 shows a teeming tube with a cooling coil;

FIG. 4 shows the arrangement of the teeming tube between a pouringvessel and an ingot mould or chill mould;

FIG. 5 shows the flow profile of a metal melt inside the teeming tube;and

FIG. 6 shows a circuit arrangement for regulating the teeming operation.

In MG. 1 the dependence of the thermal content I of a metal upon atemperature T is represented. During the cooling, first of all thatquantity of heat is withdrawn which corresponds to the course of thecurve f,. The external characteristic here is a fall of temperature, atfirst only as far as the melting point S. Upon further withdrawal ofheat the temperature T remains constant, whereas the thermal content Idiminishes further by withdrawn portion of the heat of fusion the amountQ With this amount Q it is a question of the heat of fusion. At thisjuncture the state of aggregation changes from liquid to solid.Following upon this, a reduction of the thermal content again leads to afall of temperature corresponding to the curve to. Since the withdrawalof heat depends upon the thermal conductivity of the cast material, the,thickness of the cast workpiece or ingot, and the difference oftemperature, for a given cooling power of the ingot mould or chillmould, it is to be a first approximation to be regarded as constant, andthe known equation is here applicable, where: t

d the layer already solidified in the ingot mould or chil mould; t= thetime that has so far elapsed; and k a solidification constantincorporating the aforementioned pertinent magnitudes. I

Whether the solidification of the melt sets in exactly at the meltingpoint depends upon whether sufficient crystallization nuclei areavailable. If not, then an activating energy or seedforming energy isnecessary for the formation thereof, which, however, in the case of aturbulent flow of the molten metal, is to be regarded as present.

Practical experience in filling ingot moulds or chill moulds with a meltshows clearly, as is well known, particularly in continuous casting,that this can only be effected at a speed which corresponds to thecooling power of the ingot mould or chill mould, the main influence uponthe speed of pouring being given by the thermal content of the melt. Theupper limit with respect to the permissible speed of pouring andtemperature is known, by h the occurrence of longitudinal cracks in thesolidified workpiece or ingot. They occur owing to the solidificationbeing efiected too slowly for a given cooling power of the casting mouldor chill mould in comparison with the thermal content of the melt andthe heat subsequently delivered; for the relatively thin solidifiedmarginal layer that occurs shrinks, rises out of the casting mould orchill mould, and cannot withstand the liquid pressure with which it isburn butdened, so that it fractures. As a countermeasure, the speed ofteeming is usually reduced, or, if possible, the temperature of the meltis lowered. The lower limit with respect to the speed of teeming and thetemperature is known from the occurrence of scabs on the solidifiedworkpiece or ingot. They arise from the fact that the solidification waseffected too quickly for a given cooling power of the casting mould orchill mould, in comparison with the thermal content of the melt and theheat delivered subsequently. The solidification in the marginal zone ofthe cast workpieces or ingots is here effected so quickly that theafter-flowing melt can no longer unite with the portion alreadysolidified. Regular separations of material occur. The presentinvention, in order to obviate such disturbances, provides a specialform of construction, hereinafter to be set forth, of the thermalinsulation of the melt that has entered the chill mould with a low heatcontent.

For carrying out the method according to the invention it ischaracteristic that in the heat content temperature diagram an operatingpoint W is aimed at, which is located in the portion O of the curve inFIG. i. This operating point W lies, as FIG. 1 shows, in the upperportion of the curve Qs, so that the amounts to about 5 percent thereof.

- In FIGS. 2 and 3, the teeming tube is marked 1, and the chill mould ismarked 2. The teeming tube l, which is represented in longitudinalsection, is preferably of noncircular cross section, so that the surfacearea acted upon by the cooling medium is considerably increased. Thusthe teeming tube may be made with an oval or a rectangular crosssection. A number of other cross sections of the teeming tube, to belikewise acted upon by the cooling medium, are also possible. With thisformation of the cross section of the teeming tube it is important toprovide a sufficiently large area for the withdrawal of the quantity ofheat to be removed.

The teeming tube 1 extends further, as illustrated in the drawings,preferably right to the surface level of the bath in the interior of thechill mould or casting mould. This has the advantage, on the one hand,that by the teeming tube a comparatively long cooling tract is provided,whereas on the other hand, an atmosphere of protective gas can bethereby easily maintained above the surface level of the bath in thechill mould, so that for instance a disturbing reoxidation of the moltensteel is obviated.

It is particularly advantageous to provide the teeming tube at its lowerend with a cover 3, which screens from the exterior the free crosssection of the casting mould or chill mould, which is considerablylarger than that of the teeming tribe. This constructional feature is ofparticular importance with the present invention, because the moltenmetal is brought into the chill mould 2 with a considerably lowerthermal content than is usual, and in the event of no such screeningbeing provided, there would be the risk of the formation of the socalledmatt welding," or scabs.

The teeming tube 1 consists of materials which are stable to the melt,and which also have the ample thermal conductivity requisite for thecooling. For the teeming of molten steel it is advisable, at least onthe inside of the teeming tube, to employ graphites or silicon carbide.

According to FIG. 2 the teeming tube 1 has a cooling jacket 6, whereasin FlG. 3 it is provided with a cooling coil 7. In both cases a coolingliquid 12, water for instance, is admitted into the cooling device,preferably at the point 8 in the lower part, and leaves the coolingdevice at the top, at the point 9, as indicated by arrows in thedrawings. The cooling device thereby worlcs on the known countercurrentprinciple, thus giving rise to a tendency to maintain as constant a fallof temperature as possible throughout the length of the cooling tract.

The quantity of cooling medium, and its speed of its flow, arepreferably controlled, as already described, to correspond to therequisite cooling power. The speed of pouring of the teeming jet,represented by the arrow 5, in the interior 4 of the teeming tube ll, islikewise adjusted by known means, for instance by a ladle plug, or elseby a pressure produced in the pouring vessel above the surface of themelt.

The aforementioned means for varying the cooling power and the teemingspeed include, according to FIG. 4, a regulating valve V fitted into theconnection 13 for the cooling medium 12, and a bottom plug 15 for thebottom aperture 16 of a pouring vessel 17. By this means an outlet crosssection V of variable magnitude is provided for the molten metal. Boththe plug 15, represented in FIG. 4 only by its lower portion, but inreality projecting above the pouring vessel, and also the valve V forthe connecting branch 33, may be actuated either manually or by motormeans. Adjusting it by motor means above all enables the teeming to becontrolled automatically.

The speed profile of the flow. is diagrammatically represented in FIG.5. For the turbulent state of flow it is important to exceed thecritical value of the Reynolds number, which is formed in a knownmanner, and should if possible be above 2,300. The turbulent flow has,in the direction of the cross section s, as indicated by the arrow inFIG. 5, a substantially constant speed v, as can likewise be gatheredfrom FIG. 5. The turbulent jet is largely equalized in the direction ofthe cross section sin every respect, and particularly by a temperaturewhich is practically homogeneous over the cross section, so that withoutincurring the risk of freezing up, it can to a certain extent carryalong with it even solidified metal particles, as corresponds to thewithdrawal of a part of the heat of fusion. Insofar as solidified metalparticles are formed in the immediate neighborhood of the internal wallsurface of the teeming tube 1, that is, in the so-called boundary layer,they are caught by the flow and distributed over the cross section 5. Inorder to meet reliably the risk of the formation of objectionabledeposits on the wall surface of the teeming tube 1, the speed ofteeming, and the cooling power can according to the invention be soadjusted to one another throughout the entire teeming operation that acycle is established, in which the temperature difference between twotemperature measurements located one behind another in the direction offlow in the neighborhood of the exit 10 from the teeming tube I fromtime to time is intermittently zero and different from zero. In the casein which the temperature difference differs from zero, it is found thatone is certainly not yet in the vicinity of the heat of fusion. Themolten metal therefore then runs for a short time somewhat superheatedinto the chill mould. Insofar as any deposits should have formed on theoutlet 10 from the teeming tube 1, these are now detached. Inconjunction with this, that is, when the temperature difference betweenthe said measurements of temperature is zero, heat of fusion is againwithdrawn, so that for the melt, in the middle of the withdrawal of theheat of fusion according to the invention, this is given, even if, inthe manner mentioned, this is renounced for a short time during themelting.

FIGS. 2 to 4 further show, at positions located one behind another inthe direction of flow 5 of the molten metal, temperature probes 11,which may for instance be thermocouples, or, above all, resistancethermometers. It is to be noted that for each temperature probe 11 thereare two contacts, which are connected either to the two limbs of athermocouple or else to the two ends of a resistance thermometer. Thesetemperature probes are preferably located at a short distance from theinternal wall surface of the teeming tube 1, so that they will not bedamaged by the molten metal, but on the other hand will show atemperature which at least stands in a definite relationship to thetemperature of the melt. It is not so important to determine the exacttemperature of the melt as to determine the difference of temperaturebetween two successive measuring positions, or the ratio between thetemperatures at two successive measuring points. By this means thearrangement of the temperature probes admits of being substantially lessexpensive, and at the same time they act more reliably. Thus forinstance it is possible to use, instead of costly noble metal probescapable of withstanding high temperatures, substantially cheaper probesof base metals, since owing to their distance from the teeming metal,they need only be designed for lower temperatures.

In the arrangement illustrated in FIG. 6, the temperature probes 11 areindividual temperature-measuring resistances marked 18 to 25. They areso arranged that the temperaturemeasuring resistance 18 is located nearthe outlet end 10 from the teeming tube 1, whereas the rest of thetemperature-measuring resistances are at increasing distances,corresponding to their increasing reference numerals, from the outletend 10 in the longitudinal direction of the teeming tube 1. The tem=perature-measuring resistances 18 to 25 are included in a circuit whichis equivalent to a Wheatstone bridge. To the two contacts 28 a supplyvoltage is connected. Between these two contacts there are tworesistances 26 and 27 connected in series, which are exactly equal inmagnitude. From the connection between these two resistances 26 and 27there branches off a conductor, which leads to an amplifier A. The otherentry into the amplifier A is formed by two scanning switches 29 and 30connected with one another, which enable in each case one of a number ofcontacts to be selected. To the selecting contacts of the scanningswitch 29 are connected the temperature-measuring resistances I9, 21, 23and 25, whilst to the selecting contacts of the scanning switch 30 areconnected the other temperature-measuring resistances 18, 20, 22 and 24.The other contacts of the first-mentioned group of resistances are ineach case connected with one another, and also with the outer contact ofthe resistance 27, and are fed by the same supply voltage as theresistance 27. The individual contacts of the other resistance group 18,20, 22, 24 are likewise connected with one another and also with theouter contact of the resistance 26, to be fed, together with the latter,by the supply voltage.

To the amplifier A, constructed in the usual manner, is connected arelay 31. When it is not excited, it keeps closed a circuit which is fedat the contact points 32, and in which there are a pilot lamp L and alsoa regulator C. The pilot lamp L then therefore lights up. The regulatorC controls two motors M and M which in their turn actuate two valves Vand V The motors M, and M are at first so controlled by the regulator Cas to yield a manually adjustable ratio between the opening of thevalves V and V The result is thereby obtained that at an increasedpouring speed the cooling power also rises at the same extent. Upon thiscontrol is now superimposed a control signal, which is recognizable bythe lighting of the lamp L, and in the case in which the lamp L lightsup, it leaves unaltered the adjusted ratio in the position between themotors M and M,. if however the control signal is interrupted, the motorM, is fed in such a manner that it opens the valve V more widely, so asto provide a greater cooling power. By switching means not illustrated,on the regulator C, the result can also be obtained that simultaneously,or only in the case of the absence of the control signal, the motor M,is supplied with current in such a way that it closes the valve V morestrongly, so that the teeming speed is reduced.

By the corresponding adjusting of the scanning switches 29 and 30, it ispossible to select the temperature-measuring resistances the resistance.values of which are to be compared with one another. By choosing theresistance 18 with the scanning switch 30 and the resistance 19 with thescanning switch 29, the pouring jet temperatures at the last andlast-butone positions at the outlet end of the pouring tube are comparedwith one another. The pouring operation is thus controlled in such a waythat this temperature difference is zero, and therefore a comparativelysmall portion of the heat of fu sion is withdrawn. If however theresistance 21, 23 or 25 is connected with the scanning switch 29, thepouring operation proceeds in such a way that along a correspondinglygreater section of the scanning tube, within the melt, there is nolonger any fall of temperature, and therefore a correspondingly largerpart of the heat of fusion is withdrawn.

The arrangement of a measuring instrument 35 at the outlet from theamplifier A additionally renders it possible to obtain values whichcharacterize the variation in temperature in the interior of the teemingtube 1. The knowledge of the variation in temperature may beparticularly desirable when, in consequence of the spatial arrangementof the temperature-measuring resistances within the teeming tube, and inconsequence of the distribution of temperature within the teeming tubeand/or of the zone closeto its internal wall surfaces, an exactreproduction of the position at which the temperature of the pouring jetbegins to be constant is not possible. In this case the said positionadmits of being found by also permitting a difference value differingslightly from zero, in order to produce the control signal.

Finally the scanning switches 29and 30 may still be controlled in such away that they swing to and fro for instance between two successivepositions, and thus have the result that the portion of the heat offusion withdrawn changes intermittently during the entire teemingoperation and lies, for instance, at 0 percent and 10 percent, whereby,in the manner already described, a formation of solidified deposits ofmetal at the outlet of the teeming tube is obviated.

lclaim:

l. A method of pouring superheated metal melts from a pouring vesselinto a mould having a substantial cross-sec tional area, comprising thesteps of: guiding the molten metal with a teeming tube having across-sectional area which is small compared with the cross-sectionalarea of the mould, withdrawing from the melt the whole of its superheatand a portion of its heat of fusion by cooling while it is flowingthrough the teeming tube in a state of turbulent flow with a Reynoldsnumber above the critical value, measuring temperatures corresponding tothe temperature of the melt at not less than two positions in theteeming tube located one behind another in the direction of flow of themelt, and establishing a pouring cycle in which the relationship betweenthe pouring speed and the cooling power of the mould is such that thedifference between the measured temperatures is substantial at certaintimes and is zero at other times.

2. The method of pouring superheated metals melts into moulds as claimedin claim 1, in which the points of measurement of the temperatures areclose to the outlet of the teeming ube.

3. The method of pouring superheated metal melts into moulds as claimedin claim 1, in which the points of measurement of the temperatures areclose to the outlet of the teeming tube, in which method the saidrelationship is established by adjusting the cooling power of theteeming tube.

4. The method of pouring superheated metal melts into moulds as claimedin claim 1, in which the said temperatures are measured at more than twopoints distributed along the teeming tube.

5. Apparatus for pouring superheated metal melts from a pouring vesselinto a mould, comprising a teeming tube arranged between the pouringvessel and the mould, cooling means extending over the entire length ofthe teeming tube, means for varying the teeming speed and the coolingpower relatively to one another, temperature probes located on theteeming tube at not less than two positions one behind another in thedirection of flow, and an electrical comparison circuit in which thetemperature probes are included, the circuit serving to emit a signalwhich varies as the temperature difference at said probes varies.

6. Apparatus as claimed in claim 5, in which said temperature probes aretemperature-measuring resistances included in a bridge circuit.

7. Apparatus as claimed in claim 5, further comprising automaticcontrolling means to control the said means for varying the relationshipbetween the coolingpower and the teeming speed by the signal from thecomparison circuit so that a cycle of zero difference and substantialdifference of temperature at said probes is maintained.

8. Apparatus as claimed in claim 5, in which the cross section of theteeming tube is noncircular, so as to increase the area of contactbetween its internal we wall surface and the cooling medium.

9. Apparatus as claimed in claim 5,. wherein the teeming tube extendsright to the surface of the bath of metal in the mould.

10. Apparatus as claimed in claimS, further comprising a cover at thelower end of the teeming tube, shielding from the exterior theconsiderably. larger free cross-sectional area of the mould.

1. A method of pouring superheated metal melts from a pouring vesselinto a mould having a substantial cross-sectional area, comprising thesteps of: guiding the molten metal with a teeming tube having across-sectional area which is small compared with the cross-sectionalarea of the mould, withdrawing from the melt the whole of its superheatand a portion of its heat of fusion by cooling while it is flowingthrough the teeming tube in a state of turbulent flow with a Reynold''snumber above the critical value, measuring temperatures corresponding tothe temperature of the melt at not less than two positions in theteeming tube located one behind another in the direction of flow of themelt, and establishing a pouring cycle in which the relationship betweenthe pouring speed and the cooling power of the mould is such that thedifference between the measured temperatures is substantial at certaintimes and is zero at other times.
 2. The method of pouring superheatedmetals melts into moulds as claimed in claim 1, in which the points ofmeasurement of the temperatures are close to the outlet of the teemingtube.
 3. The method of pouring superheated metal melts into moulds asclaimed in claim 1, in which the points of measurement of thetemperatures are close to the outlet of the teeming tube, in whichmethod the said relationship is established by adjusting the coolingpower of the teeming tube.
 4. The method of pouring superheated metalmelts into moulds as claimed in claim 1, in which the said temperaturesare measured at more than two points distributed along the teeming tUbe.5. Apparatus for pouring superheated metal melts from a pouring vesselinto a mould, comprising a teeming tube arranged between the pouringvessel and the mould, cooling means extending over the entire length ofthe teeming tube, means for varying the teeming speed and the coolingpower relatively to one another, temperature probes located on theteeming tube at not less than two positions one behind another in thedirection of flow, and an electrical comparison circuit in which thetemperature probes are included, the circuit serving to emit a signalwhich varies as the temperature difference at said probes varies. 6.Apparatus as claimed in claim 5, in which said temperature probes aretemperature-measuring resistances included in a bridge circuit. 7.Apparatus as claimed in claim 5, further comprising automaticcontrolling means to control the said means for varying the relationshipbetween the cooling power and the teeming speed by the signal from thecomparison circuit so that a cycle of zero difference and substantialdifference of temperature at said probes is maintained.
 8. Apparatus asclaimed in claim 5, in which the cross section of the teeming tube isnoncircular, so as to increase the area of contact between its internalwe wall surface and the cooling medium.
 9. Apparatus as claimed in claim5, wherein the teeming tube extends right to the surface of the bath ofmetal in the mould.
 10. Apparatus as claimed in claim 5, furthercomprising a cover at the lower end of the teeming tube, shielding fromthe exterior the considerably larger free cross-sectional area of themould.